The present invention the present invention relates to a method of producing a magnetic powder used in noncontact data communication of, for example, an RFID (Radio Frequency IDentification) system, a magnetic sheet production method, and an antenna module production method.
In an RFID system, a noncontact-type IC tag in which an IC chip having information recorded thereon and a resonance capacitor are electrically connected to an antenna coil is known. As the noncontact-type IC tag, there are also a card type and a type incorporated into a cellular phone and the like.
As an antenna module of the related art that is used for the noncontact-type IC tag, there is one in which a magnetic member (magnetic sheet) is arranged in a planar antenna coil that is spirally wound within a plane such that the magnetic member becomes substantially parallel to the plane of the planar antenna coil. A material having high magnetic permeability is used for the magnetic sheet used in this antenna module. With such a magnetic sheet, an inductance of the planar antenna coil becomes large, and a communication distance is elongated.
Examples of a magnetic material used for the magnetic sheet include ferrite-based magnetic materials such as a Ni—Zn-based material and a Mn—Zn-based material that have Fe as a main component. For example, by mixing and calcining raw materials of oxides such as Fe2O3, NiO, and ZnO and pulverizing them into appropriate sizes thereafter, a flat ferrite powder is produced (see, for example, Patent Document 1).
The reason why the magnetic particles are flattened is because, when a magnetic device formed of a magnetic material is used in the RFID system, demagnetization of the magnetic particles in the material can be reduced at a time a magnetic field is applied to the magnetic material, with the result that magnetic permeability can be improved.    Patent Document 1: Japanese Patent Application Laid-open No. 2001-284118 (paragraphs [0035] to [0043], FIG. 2).